Proper operation of an audio system requires the maintenance of a correct signal phase to all speakers in the system. For optimum sound quality, a proper phase relation ship should be maintained both between each input and the signal processor (e.g., amplifier) as well as between the signal processor and each output. A positive pulse amplitude at a system input should produce a corresponding positive pulse amplitude at each system output, such as each speaker driver and the acoustic output signal from each speaker. If a phase reversal occurs, the input may still produce an intelligible output, but the output will experience a deterioration in sound quality.
Similarly, each speaker should be in phase with all of the other speakers. If two or more speakers are out of phase with each other, the acoustic waves from different speakers will experience destructive interference and the sound quality will be seriously degraded.
While maintenance of proper phase relationships among audio signals should be technologically feasible, in practice this is a significant problem. The problem is particularly acute when modular units in an audio system are acquired from different manufacturers. There are no uniformly adopted standards for maintaining correct signal phase across connector jacks or even between inputs and outputs. Consequently, it is not unusual to find that phase polarities have been reversed between different speakers within a system or even between components within a system.
Recording systems with multiple microphones should be phased such that a positive pressure change (increase in pressure) at each microphone will produce a positive voltage into the recording system and, ultimately, a positive pressure change at each speaker output upon playback. The lack of standards for manufacturing cable connectors can cause polarity connection errors which must be corrected before a recording session begins.
While systems do exist to detect phase reversals, these systems tend to be relatively expensive. Such detectors are particularly expensive in the context of a nonprofessional who may change an audio system relatively infrequently to add a new component or update an existing component. A need thus exists for apparatus and methods to quickly and inexpensively check the phases of audio signals at or between various locations in an audio system, whether for a home system having relatively few audio sources and speakers or for a professional system, such as an audio mixing system or an amphitheater or auditorium having multiple sources and speakers.